1. Field of the Invention
The present invention relates to a method and apparatus for cutting the rolls of a plural-roll rolling mill without removing the rolls from the rolling mill.
2. Description of the Related Art
Methods of rolling wire rods and steel bars in sizing mills can be grouped according to the number of pairs of rolls used in a stand; i.e., two-roll, three-roll and four-roll methods. As shown in FIGS. 1A-1C, such methods involve rolling a material M through a plurality of passes by pairs of rolls (R, R') whose peripheral surfaces are provided with grooves (G, G') formed to predetermined sectional shapes. In general, dimensional accuracy of the product increases with the number of rolling pairs employed.
A four-roll rolling method is disclosed in, for example, Japanese Patent Application Laid-Open No. 6(1994)-63601 and U.S. Pat. No. 5,363,682. Since the surface of the roll calibers is worn or roughed after a time, the calibers are usually recut to enable reuse of the rolls.
The calibers are conventionally recut by removing the rolls from the rolling mill. However, the conventional method deteriorates mill productivity since dismounting and remounting the rolls requires the stoppage of rolling operations and consumes much time. Further, detaching and reattaching the rolls is a dangerous operation that requires considerable skill and manpower. Japanese Patent Application Laid-Open No. 63(1988)-237801 and the document "Precise Rolling of Steel Bars by Three-Directional Finishing Rolls" (Symposium on Plastic Working, Vol. 139, pages 23-29, 1991) disclose means for cutting roll calibers while the rolls are mounted.
Japanese Patent Application Laid-Open No. 63(1988)-237801 discloses a method of cutting the stand-mounted rolls of a two-roll rolling mill. According to the method, the rolling mill is removed from a rolling line and is horizontally aligned by fixing the position of the rolling mill through use of a pusher. The backlash of the roll is removed by rotating the roll while simultaneously pushing the roll in the thrust direction of a roll axis. A radial preload mechanism prevents radial movement of the roll. However, since the roll to be cut is not pushed toward a pass line, the roll has backlash in the direction of the pass line which greatly disperses the cutting margin of the roll.
The method disclosed in "Precise Rolling of Steel Bars by Three-Directional Finishing Rolls" (in FIG. 5, page 26) is a method for cutting the rolls of a three-roll type rolling mill. According to the method, the caliber of each of the rolls is ground while removing the backlash of the roll by inserting a conical grinding stone (ring cutting tool) between the three rolls. However, grinding the caliber serves to increase machining time, and the grinding itself requires considerable skill because the machined shape of a roll is changed by the wear caused by the cutting tool. Moreover, the method does not describe any means by which the rolls of the rolling mill can be cut as mounted on the rolling mill, particularly on a four-roll rolling mill.
Accordingly, an object of the present invention is to provide a method and apparatus by which the rolls of a plural-roll rolling mill can be cut as mounted on the rolling mill.